A primer composition is a primary explosive composition that is used to initiate or ignite another explosive composition, propellant, or charge. This other explosive composition, propellant, or charge is referred to herein as a so-called “main” explosive composition. The primer composition is more sensitive to impact and friction than the main explosive composition. The main explosive composition is relatively stable and does not ignite until initiated by the primer composition.
Many ingredients of conventional primer compositions are chronically toxic and their use is regulated by the Environmental Protection Agency. These ingredients include styphnate and picrate salts, heavy metal compounds, or diazodinitrophenol (“DDNP” or dinol). The regulated metal compounds include compounds of mercury, lead, barium, antimony, beryllium, cesium, cadmium, arsenic, chromium, selenium, strontium, or thallium. When combusted, a primer composition that includes one of these ingredients emits toxic lead oxides or toxic compounds of other heavy metals, such as oxides of cesium, barium, antimony, or strontium. DDNP is also hazardous because it is known to cause allergic reactions and is possibly carcinogenic, as identified by The Centers for Disease Control and Prevention/Agency for Toxic Substances and Disease Registry (“CDC”). Some combustion products are gaseous and are inhaled by a user of ordnance when used in applications such as small caliber ammunition that includes the primer composition. Other gaseous combustion products are typically in the form of dust or oxides of the toxic compounds mentioned above. Since small caliber ammunition is fired in large quantities in indoor and outdoor ranges for training or practice, as well as for hunting, sporting events (trap shooting, biathlon, etc.) and military simulations, the user of small caliber ammunition is potentially exposed to large amounts of these toxic combustion products.
To reduce health and environmental risks, primer compositions that are free of lead have been developed. U.S. Pat. No. 4,522,665 to Yates, Jr. et al. discloses a percussion primer that includes titanium and potassium perchlorate. U.S. Pat. No. 5,417,160 to Mei et al. discloses a percussion primer that contains calcium silicide, DDNP, and an alkaline or alkaline earth nitrate. U.S. Pat. No. 5,167,736 to Mei et al. discloses a percussion primer that includes DDNP and boron and U.S. Pat. No. 5,567,252 to Mei et al. discloses a percussion primer that includes DDNP, boron, and iron oxide. U.S. Pat. Nos. 4,963,201 and 5,216,199 to Bjerke et al. disclose a percussion primer that includes DDNP, strontium nitrate, tetracene, and a nitrate ester fuel. U.S. Pat. No. 6,478,903 to John, Jr. et al. discloses a percussion primer that includes bismuth sulfide and potassium nitrate or zinc sulfide and aluminum nitrate. U.S. Pat. No. 4,581,082 to Hagel et al. discloses a primer charge that includes zinc peroxide, DDNP, and/or a strontium salt of mono- and/or dinitrodihydroxydiazobenzene. U.S. Pat. No. 5,831,208 to Erickson discloses a lead-free, centerfire primer that includes barium nitrate, a primary explosive, a sensitizer, a nitrated ester, an abrasive sensitizer, a fuel, and a binder.
Red phosphorus has also been used in primer compositions. Red phosphorus is an allotrope of phosphorus that has a network of tetrahedrally arranged groups of four phosphorus atoms linked into chains. White phosphorous is another allotrope that is much more reactive and toxic than red phosphorous. Red phosphorus-based primer compositions were determined to be unsatisfactory by the U.S. Army Ordnance Department due to the chemical instability of the red phosphorus, which produced corrosive by-products capable of corroding metal components. U.S. Pat. No. 2,970,900 to Woodring et al. discloses a purportedly noncorrosive, priming composition that includes red phosphorus, a secondary explosive, and an oxidizing agent. The red phosphorus is stabilized by treatment with acid, elutriation, and coating with aluminum hydroxide. The secondary explosive is pentaerythritol tetranitrate (“PETN”), trimethylenetrinitramine, trinitrotoluene (“TNT”), or combinations thereof. The oxidizing agent is barium nitrate, potassium nitrate, lead nitrate, lead dioxide, basic lead nitrate, or a barium nitrate-potassium nitrate double salt. U.S. Pat. No. 2,194,480 to Pritham et al. discloses a purportedly noncorrosive, priming composition that includes red phosphorus, a fuel, such as zirconium, and an oxidizer, such as barium nitrate, strontium nitrate, basic lead nitrate, lead peroxide, or antimony sulfide. U.S. Pat. No. 2,649,047 to Silverstein discloses a primer that includes a primer composition and a metal cup. The primer composition includes red phosphorus and barium nitrate. The metal cup is formed from a metal or coated with a metal that is less catalytically active than nickel, such as aluminum, aluminum alloys, zinc, chromium, cadmium, lead, tin, lead/tin alloys, or Duralumin. U.S. Pat. No. 2,231,946 to Rechel et al. discloses a propellant powder that includes a small amount of red phosphorus, which inhibits erosion of the gun barrel.
Red phosphorus-based compositions have also been used as smoke-producing or obscurant compositions. These compositions typically include an excess amount of red phosphorus relative to oxidizing agent and utilize oxygen in the atmosphere to enhance the production of smoke. Upon ignition, these red phosphorus-based compositions provide low amounts of heat, sufficient to cause the red phosphorus to smolder, producing aerosol particles and dense smoke.
Red phosphorus is relatively stable in air and is easier to handle than other allotropes of phosphorus. However, if red phosphorus is exposed to oxygen (“O2”), water (“H2O”), or mixtures thereof at elevated temperatures, such as during storage, the red phosphorus reacts with the O2 and H2O, releasing phosphine (“PH3”) gas and phosphoric acids (H3PO2, H3PO3, or H3PO4). As is well known, the PH3 is toxic and the phosphoric acids are corrosive. To improve the stability of red phosphorus in environments rich in O2 or H2O, dust suppressing agents, stabilizers, or microencapsulating resins have been used. The dust suppressing agents are liquid organic compounds. The stabilizers are typically inorganic salts, such as metal oxides. The microencapsulating resins are thermoset resins, such as epoxy resins or phenolic resins. Currently, microencapsulating resins are not used in military phosphorus applications. The military specification for phosphorous has been deactivated and is not expected to be updated to include encapsulation.
Red phosphorus has also been used as a flame retardant in a polymer-based composition, as disclosed in U.S. Pat. No. 4,698,215 to Albanesi et al. The red phosphorus is stabilized by coating particles of the red phosphorus with a first layer of aluminum hydroxide and a second layer of a urea-melamine-phenol-formaldehyde resin. Red phosphorus has also been used in a pyrotechnic composition to block infrared radiation and visible light, as disclosed in U.S. Pat. No. 4,728,375 to Simpson. The red phosphorus is stabilized by dispersing the red phosphorus in a rubber.